Various types of fluid/powder applicator devices for use with animals are known in the prior art. However, what is needed is a pet door fluid/powder applicator device disposed upon the bottom of the flap of a typical pet door, said pet door fluid/powder applicator device including at least one roller volubly disposed on an underside of a chamber, at least one interior cavity disposed within said chamber, said cavity configured to store fluid/powder additional thereto in contact with a first poriton of the roller, wherein said fluid/powder is applied to the hide of an animal as said animal is caused to contact the at least one roller, and rotate said roller thereby, whenever said animal moves through the pet door, whereby a dosage of the fluid/powder containing a desired active ingredient is applicable to the animal.